AbstractCrystalline polymers consist of regions of varying order ranging from perfectly crystalline to random and rubber‐like assemblies of polymer chains. Such structures may thus be represented in terms of statistical parameters characterizing the size and shape of ordered regions, degree of order and orientation of these regions. These parameters may be characterized by such techniques as x‐ray and light scattering. A study of the deformation of such polymers requires the specification of the change in these descriptive parameters with time, temperature, and morphology. The application of a number of optical techniques to this determination is discussed and typical results are presented. A deformation mechanism for crystalline polymers is proposed which is consistent with these observati